This invention relates to fluid collection devices and more particularly to liquid collection devices having means for partitioning separated lighter and heavier phases of the liquid.
In the testing of blood samples, for example, whole blood is usually drawn into an evacuated collection tube and then the tube is placed in a centrifuge for separating the lighter phase, serum or plasma, and the heavier or cellular phase so that the individual phases may be isolated and tested. Many different types of phase partitioning devices which provide a barrier or seal between the separated phases have been used or proposed for the purpose of allowing the lighter phase to be decanted or poured into a transfer tube free of cells or to enable the two phases to remain in the collection tube without intermixing during shipment to a laboratory where the lighter phase is removed and subjected to analysis.
With some phase separation or partitioning devices, the stopper of the sampling tube, after the light and heavy phases have been separated in a centrifuge, is removed and the light phase is drawn or siphoned off. In some cases, a barrier member is inserted into the tube that allows the light phase to pass by it and which is stopped at the interface of the two phases to provide a seal between the phases. These methods require the opening of the sampling tube after the phases are separated with the possibility of causing them to be intermixed. Also, it is time consuming and subjects the personnel to the possibility of coming in contact with a virus or the like, such as hepatitis.
Other types of separation devices have been used such as disclosed in U.S. Pat. No. 3,852,194 wherein a gel, such as silicone gel, is disposed in the tube. The gel has a specific gravity intermediate the light and heavy phases so that during centrifugation, it automatically moves to the interface of the separated phases to provide a seal. One disadvantage of this type of partitioning system is that the gel may affect the liquid. For example, silicone oil may enter the light phase and cause clogging in the serum or plasma testing equipment. In U.S. Pat. No. 3,814,248, a spool and ball partitioning device is disclosed. One of the problems of this device is that there are two different seals required, one between the spool and the wall of the tube, and the other between the ball and the spool, and this increases the danger of cells passing into the lighter phase to contaminate it. In U.S. Pat. No. 3,508,653, a deformable piston member having a specific gravity intermediate those of the separated phases is attached to the stopper and after centrifugal separation of the phases, the centrifuge is speeded up to cause the piston to separate from the stopper and move to the interface. One of the disadvantages of the latter type of device is that the centrifuge must be controlled to operate at two different speeds.